This invention relates to electronic devices, and, more particularly, to electrostatic discharge protection devices and methods.
Many electronic components, such as integrated circuits, MOS transistors, diodes, and thin film capacitors are sensitive to electrostatic discharge (ESD) and may be damaged during handling. Indeed, the gate oxide in CMOS integrated circuits may be on the order of 200 .ANG. thick and will breakdown at 15-20 volts between the gate and the transistor substrate. Of course, this 15-20 volts greatly exceeds the normal operating voltage, and built-in ESD protection may prevent damage from somewhat higher voltages transiently applied to integrated circuit package pins. But, during handling, electrostatic buildup on a person walking across a room can easily reach 15,000 to 20,000 volts. This high voltage arises from the electric charge generated by rubbing two dissimilar materials together (triboelectric charging effect). The discharge of triboelectric charge into the pins of a packaged transistor or integrated circuit may damage the circuit sufficiently to cause immediate failure or to weaken the circuit to cause subsequent early failure. And on-chip ESD protection devices do not provide sufficient protection without overly encumbering the electrical characteristics (i.e., protection diodes introduce capacitance and protection resistors add to RC time delays).
One approach to providing ESD protection employs conductive clothing for individuals handling ESD sensitive items plus conductive grounded wrist straps and ground mats for discharging accumulated electrostatic charge. However, this approach has problems including the expense of providing electrically conductive clothing or walkways and the ambulatory limits imposed by wrist strap tethering.